I want to group the common methods in one file and use it. For example, login to a page using selenium may be used in multiple times. Define that in class A and call it in class B. However, it throws null pointer exception.

class A has

public void test_Login() throws Exception
    {
        try{
        selenium.setTimeout("60000");
        selenium.open("http://localhost");
        selenium.windowFocus();
        selenium.windowMaximize();
        selenium.windowFocus();
        selenium.type("userName", "admin");
        selenium.type("password", "admin");
        Result=selenium.isElementPresent("//input[@type='image']");
        selenium.click("//input[@type='image']");
        selenium.waitForPageToLoad(Timeout);
        }
        catch(Exception ex)
        {   
            System.out.println(ex);
            ex.printStackTrace();
        }
    }

with all other java syntax

in class B

public void test_kk() throws Exception
    {

        try
        {
            a.test_Login();
        }
        catch(Exception ex)
        {
            System.out.println(ex);
            ex.printStackTrace();
        }
    }

with all syntax.

When I execute class B, I got this error,

java.lang.NullPointerException
        at A.test_Login(A.java:32)
        at B.test_kk(savefile.java:58)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
        at java.lang.reflect.Method.invoke(Unknown Source)
        at junit.framework.TestCase.runTest(TestCase.java:168)
        at junit.framework.TestCase.runBare(TestCase.java:134)
        at com.thoughtworks.selenium.SeleneseTestCase.runBare(SeleneseTestCase.j
ava:212)
        at junit.framework.TestResult$1.protect(TestResult.java:110)
        at junit.framework.TestResult.runProtected(TestResult.java:128)
        at junit.framework.TestResult.run(TestResult.java:113)
        at junit.framework.TestCase.run(TestCase.java:124)
        at junit.framework.TestSuite.runTest(TestSuite.java:232)
        at junit.framework.TestSuite.run(TestSuite.java:227)
        at junit.textui.TestRunner.doRun(TestRunner.java:116)
        at junit.textui.TestRunner.doRun(TestRunner.java:109)
        at junit.textui.TestRunner.run(TestRunner.java:77)
        at B.main(B.java:77)

I hope someone must have tried this before. I may miss something here.